Disk drives are commonly used in microprocessor based electronic devices, such as workstations, personal computers, laptops and other computer systems, to store and retrieve large amounts of data. A typical disc drive includes a plurality of magnetic discs that are rotated by a spindle motor and an actuator arm assembly that includes read/write heads mounted to flexure arms. An actuator motor (e.g., voice coil motor) can rotate the flexure arms and heads about a pivot bearing relative to the disks. The heads are configured to fly upon air bearings in very close proximity to the rotating disks.
The surface of each disc is divided into a series of data tracks which are spaced radially from one another across a band having an inner diameter and an outer diameter. The data tracks extend circumferentially around the discs and store data in the form of magnetic flux transitions on the disc surfaces. Each data track is divided into a number of data sectors that store fixed sized blocks of user data. Embedded among the data sectors on each track are servo fields that define servo information that enables the disc drive to control the radial position of the heads relative to tracks on the discs and to determine the circumferential location of the heads.
The servo fields are written to the discs during the manufacture of a disc drive using a highly precise servo track writer, which utilizes the heads of the disc drive to write the servo fields. As the servo fields are used to define the tracks, it is important to precisely control the position of the heads as the servo fields are written to the disc surfaces. Thus, a typical servo track writer includes a positioning system which advances the position of the heads, a position detector which estimates the position of the heads and control circuitry which provides the servo information to be written as the servo fields on the disks.
In one type of servo track writer, the positioning system includes a push pin assembly that engages the actuator arm assembly through an opening in the disc drive base deck. A positioner moves the push pin to radially position the heads while the servo fields are written on the disk.
As will be recognized, proper radial alignment of the servo fields is essential to facilitate reliable operation of the disc drive. For example, when errors are introduced in the placement of the servo fields, components at corresponding frequencies can appear in a position error signal (PES) generated by the servo system during subsequent operation of the drive. The PES is a measure of the relative position of a selected head with respect to an associated track, and is used primarily during track following operations to maintain the head over the center of the track. Thus, such frequency components appearing in the PES for a selected track will result in the repeated adjustment of the position of the head by the servo system in an attempt to maintain the head over the center of the track during each revolution of the disc. When such frequencies are sufficiently severe, the correction required to account for these frequencies may use an unacceptable amount of the bandwidth of the servo system and/or may limit the overall track density that can be obtained on the disks.
It is known that the excitation of system resonances of the servo track writer can result in oscillations at the heads, leading to errors in the placement of the servo fields and causing corresponding frequency components to be generated in the PES during subsequent disc drive operation. System resonances can be excited from, for example, vibrations generated by the operation of the disc drive spindle motor and/or wind buffeting of the actuator arm assembly (referred to as windage) during rotation of the discs as the servo fields are written.
Attempts to minimize the effects of system resonances have included efforts to stiffen the push-pin and the associated push-pin assembly, as well as installing a soft, energy-absorbing material between the push-pin and the actuator arm assembly. However, to date such efforts have not been completely successful in eliminating the effects of resonances during the writing of the servo fields. Moreover, as disc drive track densities increase, greater demands are placed upon servo track writers to accurately locate the servo fields on the discs; thus, vibration levels that were acceptable for earlier generations become increasingly unacceptable for later generations of drives.
Accordingly, there is a need for an improved approach to reducing the effect of system resonances in a disc drive servo track writer in order to reduce or eliminate the effects of frequency components in a PES generated from the servo fields during subsequent disc drive operation.